We have recently demonstrated that gene targeting via homologous recombination in zebrafish is feasible (Zuatal, Nature Methods, 2013). Homologous recombination in zebrafish with a dsDNA donor makes it possible to knock-in variants of human genes of rare and undiagnosed diseases into zebrafish genome. We have selected four such genes that are conserved between zebrafish and human for genomic knock-in studies. These zebrafish models should facilitate the understanding of genetics, biochemistry and pathophysiology of these newly diagnosed disease genes.